Abstract
Invasive exotic plants often threaten the establishment of desirable plants in vegetation restoration projects. There is little understanding of the role of intraspecific genetic variation in resident natives in allowing or resisting invasions. Spotted knapweed (Centaurea maculosa [= C. stoebe]) is one of the most abundant invaders in western North American grasslands. We hypothesized that there was genetic variation in local populations of bluebunch wheatgrass (Agropyron spicatum [= Pseudoroegneria spicata]), a dominant native, for resistance to spotted knapweed and that we could identify resistant wheatgrass plants by locating isolated survivors in knapweed-infested grasslands. We planted clones of 12 “survivor” wheatgrass plants, four haphazardly chosen “unexposed” plants from uninvaded grasslands, and one cultivar (Goldar) selected for vigorous growth in a knapweed-dominated field and followed survival, growth, and reproduction for three years. We also raised clones of these same families in pots with knapweed in a complete randomized block design. Size, growth, and reproductive effort of wheatgrass plants varied among families in the field study where canopy cover of knapweed was more than 30 percent. Much of the variation among wheatgrass families was attributed to the superior performance of Goldar, which had greater growth, fecundity, and knapweed suppression compared with unexposed families in the field and garden studies. Our strategy for identifying knapweed-tolerant genotypes was ineffective; survivor families did not grow better than unexposed controls in the field or garden study. Our conclusion: developing local cultivars similar to Goldar by selecting for vigor and productivity among wild, local collections may be the best way to develop restoration cultivars that tolerate and suppress invasive weeds.
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